body {
  font-family: 'Segoe UI', sans-serif;
  background-color: #3d3d3d;
  color: #ffffff;
  text-align: center;
  margin: 0;
  padding: 20px;
}

h1 {
  font-size: 28px;
  margin-bottom: 10px;
}

.container {
  max-width: 320px;
  margin: 0 auto;
  padding: 20px;
  background-color: #6a7576;
  border-radius: 12px;
  box-shadow: 0 0 12px rgba(0, 255, 200, 0.2);
}

#display {
  background-color: #e6e656;
  color: #2a2a2a;
  font-size: 32px;
  padding: 12px;
  border-radius: 6px;
  margin-bottom: 16px;
  text-align: right;
  overflow-x: auto;
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

button {
  padding: 16px;
  font-size: 18px;
  background-color: #133d57;
  color: #ffffff;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  transition: 0.2s ease;
}

button:hover {
  background-color: #444;
}

button:active {
  background-color: #00ffcc;
  color: #000;
}

#clear, #del {
  background-color: #ff4444;
}

#clear:hover, #del:hover {
  background-color: #ff6666;
}